Angular rate sensor and method of manufacturing the same

ABSTRACT

An angular rate sensor  100  comprises a first structure  110  which includes a fixed portion  111  having an opening  114,  a displacing portion  112  placed in the opening  114,  and a connecting portion  113  adapted to connect the fixed portion  111  and the displacing portions  112;  a second structure  130  which includes a weighting portion  132  joined to the displacing portion  112,  and a pedestal portion  131  arranged to surround the weighting portions  132  and joined to the fixed portion  111,  and is laminated in place on the first structure  110.  A first body  140  formed by laminating a first metal layer  142  and a first insulating layer  141  thereon is joined to the fixed portion  111  such that the first insulating layer  141  faces the fixed portion  111.  A second substrate  150  formed by laminating a second metal layer  152  and a second insulating layer  151  thereon is joined to the pedestal portion  131  such that the second insulating layer  151  faces the pedestal portion  131.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an angular rate sensor for detectingangular rate and a method of manufacturing the sensor.

This application is based on the prior Japanese Patent Application No.2005-156228 filed on May 27, 2005, the entire contents of which areincorporated herein by reference.

2. Background Art

The technology of angular rate sensors for detecting angular velocity byvibrating a vibrating portion and utilizing the Coriolis force based onthe angular rate has been developed (Patent Document 1).

Patent Document 1: TOKUKAI No. 2002-350138, KOHO

In the aforementioned technology, a sealing means of the vibratingportion is not disclosed. It is preferred to reduce the influence of airresistance by sealing the vibrating portion, because the vibrationportion is subjected to air resistance.

However, ensuring the credibility of the sealing and attemptingminiaturization of the angular rate sensor is always associated withsome difficulty. For example, when attempting to seal the angular ratesensor using a glass substrate, the thickness tends to become large inorder to strengthen the sensor, and therefore it is difficult tominiaturize the angular rate sensor along the thickness direction.

SUMMARY OF THE INVENTION

In light of the above, it is an object of the present invention toprovide an angular rate sensor that can provide credibility of sealingand miniaturization, and a method of manufacturing such an angularsensor.

The present invention is an angular rate sensor comprising: a firststructure which includes a fixed portion having an opening, a displacingportion placed in the opening and configured to be displaced relative tothe fixed portion, and a connecting portion adapted to connect the fixedportion and the displacing portions, and is formed of a substratecomposed of a first semiconductor material; a second structure whichincludes a weighting portion respectively joined to the displacingportions, and a pedestal portion arranged to surround the weightingportion and joined to the fixed portion, and is laminated in place onthe first structure and composed of a second semiconductor material; afirst substrate laminated on the first structure; a second substratelaminated on the second structure; a vibration imparting portion adaptedto impart vibration, in a direction vertical to the first structure, tothe displacing portion of the first structure; and a displacementdetecting portion adapted to detect displacement of the displacingportion; wherein the first substrate, the fixed portion, the pedestalportion, and the second substrate form a sealed body together such thatthe displacing portion and the weighting portion can be moved in thesealed body.

The present invention is an angular rate sensor, wherein the firststructure includes a first metal layer and a first insulating layerlaminated on the first metal layer, the first insulating layer beingconnected to the fixed potion; and the second structure includes asecond metal layer and a second insulating layer laminated on the secondmetal layer, the second insulating layer being connected to the pedestalportion.

The present invention is an angular rate sensor, wherein each of thefirst insulating layer of the first substrate and the second insulatinglayer of the second substrate is composed of a material capable of beingetched.

The present invention is an angular rate sensor, wherein either of thefirst insulating layer of the first substrate or the second insulatinglayer of the second substrate has a third metal layer formed thereon.

The present invention is an angular rate sensor, wherein each of thefirst semiconductor material of the first structure and the secondsemiconductor material of the second structure is formed from silicon.

The present invention is an angular rate sensor, wherein a joiningportion is provided between the first structure and the secondstructure.

The present invention is an angular rate sensor, wherein each of thefirst semiconductor material of the first structure and the secondsemiconductor material of the second structure is formed from siliconwhile the joining portion is formed from silicon oxide.

The present invention is an angular rate sensor, wherein the vibrationimparting portion is formed of the third metal layer.

The present invention is an angular rate sensor, wherein thedisplacement detecting portion is formed of the third metal layer.

The present invention is a method of manufacturing an angular ratesensor comprising the steps of: producing a semiconductor substrate bylaminating a first layer composed of a first semiconductor material, asecond layer composed of an oxide, and a third layer composed of asecond semiconductor material, in succession; etching the first andthird layers of the semiconductor substrate to produce, from the firstlayer, a first structure which includes a fixed portion having anopening, a displacing portion placed in the opening and adapted to bedisplaced relative to the fixed portion, and a connecting portionadapted to connect the fixed portion and the displacing portions, andproduce, from the third layer, a second structure which includesweighting portions and a pedestal portion arranged to surround theweighting portions, and is laminated in place on the first structure;etching the second layer of the semiconductor substrate, in which thefirst and second structures have been produced, to produce a joiningportion including a first joining portion having an opening and adaptedto join the fixed portion to the pedestal portion, and a second joiningportion arranged in the opening of the first joining portion and adaptedto join the displacing portions to the weighting portion; and joining afirst substrate to the first structure and joining the second substrateto the second structure, by lamination, respectively.

The present invention is a method of manufacturing an angular ratesensor, wherein the first structure includes a first metal layer and afirst insulating layer laminated on the first metal layer; and thesecond structure includes a second metal layer and a second insulatinglayer laminated on the second metal layer; and wherein the firstinsulating layer of the first substrate is laminated on the firststructure, and the second insulating layer of the second substrate islaminated on the second structure.

The present invention is a method of manufacturing an angular ratesensor further comprising the steps of: attaching an adhesive filmeither on the first or second substrate; cutting an angular rate sensorfrom the semiconductor substrate and the first and second substratescorresponding to a region where the first and second structures areformed; pressing the adhesive film corresponding to the region to pushout the cut angular sensor; and sucking the pushed out angular sensor.

The present invention is a method of manufacturing an angular ratesensor, wherein a vibration imparting portion adapted to impartingvibration, in a direction vertical to the first structure, to thedisplacing portion of the first structure is provided at the same timeof laminating the first substrate on the first structure and laminatingthe second substrate on the second structure.

The present invention is a method of manufacturing an angular ratesensor, wherein either of the first insulating layer of the firstsubstrate or the second insulating layer of the second substrate has athird metal layer formed thereon; and the vibration imparting portionadapted to impart vibration, in a direction vertical to the firststructure, to the displacing portions of the first structure is formedof the third metal layer.

The present invention is a method of manufacturing an angular ratesensor, wherein either of the first insulating layer of the firstsubstrate or the second insulating layer of the second substrate has athird metal layer formed thereon; and a displacement detecting portionadapted to detect displacement of the displacing portions is formed ofthe third metal layer.

Thus, according to the present invention, an angular rate sensor thatcan provide the credibility of sealing and miniaturization, and a methodof manufacturing such an angular sensor can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an angular rate sensoraccording to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a state where a part ofthe angular rate sensor of FIG. 1 is disassembled.

FIG. 3 is a top view of a first structure.

FIG. 4 is a bottom view of a second structure.

FIG. 5 is a bottom view of a first substrate.

FIG. 6 is a top view of a second substrate.

FIG. 7 is a cross section of an angular rate sensor.

FIG. 8 is a cross section of the first substrate.

FIG. 9 is a cross section of the second substrate.

FIG. 10 is a cross section showing a state of the angular rate sensorwhen Coriolis force Fy due to angular rate ωx in the X-axis direction isapplied to the sensor.

FIG. 11 is a flow chart showing one example of a procedure of producingan angular rate sensor.

FIG. 12 is a cross section showing a state of the angular rate sensor inthe production procedure of FIG. 11.

FIG. 13 is a cross section showing another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 14 is a cross section showing another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 15 is a cross section showing still another state of the angularrate sensor in the production procedure of FIG. 11.

FIG. 16 is a cross section showing another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 17 is a cross section showing yet another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 18 is a cross section showing another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 19 is a cross section showing still another state of the angularrate sensor in the production procedure of FIG. 11.

FIG. 20 is a cross section showing yet another state of the angular ratesensor in the production procedure of FIG. 11.

FIG. 21 is a perspective view showing a semiconductor substrate.

FIG. 22 is a perspective view showing a state where a dicing pad isattached to a bottom face of the semiconductor substrate and laminatedproducts.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment according to the present invention will be described indetail with reference to the drawings.

FIG. 1 is an exploded perspective view showing a state where an angularrate sensor 100 is disassembled.

The angular rate sensor 100 comprises a first structure 110, a joiningportion 120, a second structure 130, a first substrate 140, and a secondsubstrate 150, which are laminated in place with one another.

FIG. 2 is an exploded perspective view showing a state where a portion(the first structure 110 and the second structure 130) of the angularrate sensor 100 is further disassembled. FIG. 3 is a top view of thefirst structure 110, and FIG. 4 is a bottom view of the second structure130. FIG. 5 is a bottom view of the first substrate 140, and FIG. 6 is atop view of the second substrate 150. FIG. 7 is a cross section showinga state where the angular rate sensor 100 is cut along line A1-A2 ofFIG. 1. FIGS. 8 and 9 are cross sections showing states where the firstand second substrates 140, 150 are cut along line B1-B2 of FIG. 5 andline C1-C2 of FIG. 6, respectively.

It is noted that in FIGS. 1 and 2 the depiction of electrodes which willbe described below is omitted for clearness.

The angular rate sensor 100 is sealed and has a reduced pressure in theinterior. This is because such a reduced pressure serves to decrease airresistance upon vibration of displacing portions (vibrating portion) 112which will be described below. Upon vibration of the displacing portions112 in the Z-axis direction, Coriolis Force Fy, Fx in the Y-axis orX-axis direction due to angular velocity (angular rate) ωx, ωy in theX-axis or Y-axis direction will be applied to the displacing portions112. Thus, by detecting of displacement of the displacing portions 112due to the Coriolis Force Fy, Fx applied thereto, it is possible tomeasure the angular velocity (angular rate) ωx, ωy. In this way, theangular rate sensor 100 can measure these two-axis angular velocitiesωx, ωy. This will be described below in more detail.

Each of the first structure 110, joining portion 120, second structure130, first substrate 140, and second substrate 150 has an outerperiphery of, for example, a generally square shape having each side of1 mm, and they have heights of 3 to 12 μm, 0.5 to 3 μm, 600 to 725 μm,30 to 150 μm, and 30 to 150 μm, respectively.

The first structure 110, joining portion 120, and second structure 130are formed from silicon, silicon oxide, and silicon, respectively, thusbeing produced integrally using an SOI (Silicon On Insulator) substratehaving a silicon/silicon oxide/silicon three-layered structure. Thefirst substrate 140 and the second substrate 150 are made of laminatedproducts formed of a resinous material and a metal, respectively.

The first structure 110 is formed of a substrate having a contour of agenerally square shape, and includes a fixed portion 111, displacingportions 112 (112 a to 112 e), and connecting portions 113 (113 a to 113d). The first structure 110 is made by etching a film of a semiconductormaterial to form openings 114 (114 a to 114 d).

The fixed portion 111 is formed of a substrate having an outer peripheryand an inner periphery (opening) both having a generally squareframe-like shape.

The displacing portions 112 comprise displacing portions 112 a to 112 e.The displacing portion 112 a is a substrate having a generallysquare-shaped outer periphery, and is located around the center of theopenings 114 a of the fixed portion 111. The other displacing portions112 b to 112 e are also formed, respectively, of substrates each havinga generally square-shaped outer periphery, and arranged such that theyare connected with and surround the displacing portion 112 a on allsides (in the positive X-axis, negative X-axis, positive Y-axis, andnegative Y-axis directions). The displacing portions 112 a to 112 e arejoined, respectively, via the joining portion 120 to weighting portions132 a to 132 e which will be described below, and displaced integrallyrelative to the fixed portion 111.

On the displacing portions 112 a to 112 e, driving electrodes 115 (115 ato 115 e) and detecting electrodes 116 (116 b to 116 e) are disposed,respectively. Though not shown, the driving electrodes 115 and thedetecting electrodes 116 are connected with terminals provided on thefixed portion 111 via wires running through the connecting portions 113,respectively.

Each of the driving electrodes 115 is in a capacitive coupling relationto the corresponding one of driving electrodes 146 provided on a rearface of the first substrate 140, which electrodes 146 will be describedbelow. The voltage to be applied during the capacitive coupling willcause vibration of the displacing portions 112 in the Z-axis direction.Also, each of the detecting electrodes 116 is in a capacitive couplingrelation to the corresponding one of detecting electrodes 147 providedon a rear face of the first substrate 140, which electrodes 147 will bedescribed below. Using the change in capacitance during the capacitivecoupling, the displacements in the X-axis and Y-axis directions of thedisplacing portions 112 are detected. The driving operation anddetection will be further described below.

The connecting portions 113 a to 113 d are substrates each having agenerally rectangular shape, and adapted to connect the fixed portion111 and the displacing portions 112 on all sides (in the directions of45°, 135°, 225° and 315°, assuming that the X-axis direction is 0° inthe X-Y plane), repespectively.

Each of the connecting portions 113 a to 113 d functions as a bendablebeam. Such bending of the connecting portions 113 a to 113 d enables therespective displacing portions 112 to be displaced relative to the fixedportion 111. Specifically, the displacing portions 112 are linearlydisplaced in the positive Z-axis and negative Z-axis directions relativeto the fixed portion 111, respectively. Also, the displacing portions112 can effect both positive and negative rotations about both of the Xaxis and the Y axis relative to the fixed portion 111. Namely, as usedherein, the term “displacement” may include both movement and rotation(i.e., movement in the Z axis and rotations in the X and Y axes).

The second structure 130 is formed of a substrate having a contour of agenerally square shape, and includes a pedestal portion 131 and theweighting portions 132 (132 a to 132 e). The second structure 130 isproduced by making openings 133 through etching a substrate of asemiconductor material. The pedestal portion 131 and the weightingportions 132 are of an approximately equal height, separated from eachother by the openings 133, and movable relatively.

The pedestal portion 131 is formed of a substrate having an outerperiphery and an inner periphery (opening) both having a generallysquare frame-like shape. The pedestal portion 131 has a shapecorresponding to the fixed portion 111, and is connected to the fixedportion 111 via the joining portion 120.

Each of the weighting portions 132 has a mass suitable for serving as aweight or working body to receive Coriolis force due to angularvelocity. That is, when angular velocity is applied, Coriolis force willwork on the center of gravity of the weighting portions 132.

The weighting portions 132 are divided into weighting portions 132 a to132 e each having a generally rectangular shape. The surroundingweighting portions 132 b to 132 e are connected to the centrally placedweighting portion 132 a on all sides, enabling integral displacement(movement and rotation) as the whole body. Namely, the weighting portion132 a functions as a connecting portion for connecting the weightingportions 132 b to 132 e.

Each of the weighting portions 132 a to 132 e has a generally squarecross section corresponding to each of the displacing portions 112 a to112 e, and is joined to each of the corresponding displacing portions112 a to 112 e via the joining portion 120. The displacing portions 112are displaced corresponding to the Coriolis force to be applied to theweighting portions 132, thus enabling measurement of the angularvelocity.

The aim of constructing the weighting portions 132 consisting of theweighting portions 132 a to 132 e is to achieve compatibility ofminiaturization and sensitization of the angular rate sensor 100. Thatis, the miniaturization of the angular rate sensor 100 can lead toreduction of the volume of the weighting portions 132, thus decreasingtheir mass. Therefore, this may lower the sensitivity to the angularvelocity. According to the present invention, dispersed arrangement ofthe weighting portions 132 b to 132 e without affecting the bendingproperties of the connecting portions 113 a to 113 d servesadvantageously to ensure to provide an adequate mass of the weightingportions 132. As a result, the compatibility of the miniaturization andsensitization of the angular rate sensor 100 can be realized.

On the rear face of the weighting portion 132 a is provided a drivingelectrode 135. The driving electrode 135 is in a capacitive couplingrelation to a driving electrode 156 provided on the top face of thesecond substrate 150. The electrode 156 will be described below. Thevoltage to be applied during the capacitive coupling will causevibration of the displacing portions 112 in the Z-axis direction. Thedriving operation will be further described below.

The joining portion 120, as describe above, connects the first andsecond structures 110, 130. The joining portion 120 is divided into afirst joining portion 121 for connecting the fixed portion 111 and thepedestal portion 131, and second joining portions 122 (122 a to 122 e)for connecting the displacing portions 112 a to 112 e and the weightingportions 132 a to 132 e, respectively. Other than these portions, thefirst and second structures 110, 130 have openings 114, 133 so as toenable the bending of the connecting portions 113 a to 113 d and thedisplacement of the weighting portions 132.

The joining portions 121, 122 can be constructed by etching a siliconoxide film.

The first substrate 140 has an outer periphery of a substantiallyrectangular shape and includes a substrate body 141 and a reinforcingportion 142. The substrate body 141 has a frame portion 143 and a bottomplate portion 144. The substrate body 141 is made by forming a recess145 having a generally rectangular shape (for example, with a width andheight of 800 μm and a depth of 10 μm) in the substrate.

The frame portion 143 is formed of a substrate having outer and innerperipheries each having a generally square frame-like shape. The frameportion 143 has a shape corresponding to the shape of the fixed portion111, and is joined to the fixed portion 111 by various means (forexample, adhesives or alloys).

The bottom portion 144 is formed of a substrate having an outerperiphery of a generally square shape which is substantially the same asthe shape of the frame portion 143.

Forming the recess 145 in the substrate 140 is aimed to ensure toprovide a space required for displacement of the displacing portions112. Alternatively, in place of forming the recess 145 in the substrate140, or in addition to the recess 145, it is also possible to make thefixed portion 111 different in height or thickness from the displacingportions 112. For example, making the thickness of the displacingportions 112 smaller than that of the fixed portion 111 can ensure toprovide the space in which the displacing portions 112 can be displaced.

The reinforcing portion 142 is formed of a substrate having an outerperiphery of a generally square shape, and is joined to the substratebody 141 by various means (for example, adhesives). The reinforcingportion 142 serves to enhance mechanical strength of the first substrate140 and reduce gas permeability of the first substrate 140.

For example, in the case where the main component of the substrate body141 is a resinous material (for example, a polyimide material), thethickness of the substrate body 141 must be increased to an extent so asto ensure to impart adequate strength to the first substrate 140. Inaddition, permeation of an external gas through the first substrate 140may degrade the degree of vacuum in the interior of the angular ratesensor 100.

To address such challenges, a material, for example, a metal having highstrength and non-gas-permeable properties can be used as the materialfor constituting the reinforcing portion 142 so as to ensure with easeto impart sufficient strength and non-gas-permeability to thereinforcing portion 142. As a result, it becomes easy to reduce thethickness of the first substrate 140 (i.e., miniaturize the angular ratesensor 100) as well as to decrease the gas permeability (i.e., lengthenthe life span of the angular rate sensor 100).

Driving electrodes 146 (146 a to 146 e) and detecting electrodes 147(147 b to 147 e) are provided on the bottom plate portion 144 (on therear face of the first substrate 140). To the driving electrodes 146 anddetecting electrodes 147 are connected terminals 148, 149, respectively.A through-hole is formed in the bottom plate portion 144 and reinforcingportion 142 for enabling electric connection from the exterior of theangular rate sensor 100 to the terminals 148, 149.

Each of the driving electrodes 146 a to 146 e is in a capacitivecoupling relation to the corresponding one of the driving electrodes 115a to 115 e, and the voltage to be applied during the capacitive couplingwill cause vibration of the displacing portions 112 in the Z-axisdirection. Also, each of the detecting electrodes 147 b to 147 e is in acapacitive coupling relation to the corresponding one of detectingelectrodes 116 b to 116 e. Using the change in capacitance during thecapacitive coupling, the displacements in the X-axis and Y-axisdirections of the displacing portions 112 are detected. The drivingoperation and detection will be further described below.

As the substrate body 141, a resinous material, for example, polyimidecan be used. In this case, the recess 145 can be formed by wet-etchingthe polyimide substrate using an etching solution (for example, analkali-amide type etching solution). Thereafter, the driving electrodes146 and the detecting electrodes 147 are formed.

Alternatively, as the substrate body 141, a laminated material composedof a resin substrate (first insulating layer) (for example, polyimide)141 a and a metal substrate (second insulating layer) (for example,copper) 141 b can be used. In such a case, by wet-etching the metalsubstrate 141 b by an etching solution (for example, an aqueous FeCl₃solution), the recess 145 can be produced. Further, the bottom face ofthe frame portion 143 will be formed of the metallic material. Also, thereinforcing portions 142 will be a first metal layer.

The metal substrate 141 b can be also used as a material forconstituting the driving electrodes 146 and detecting electrodes 147. Inthis case, the metal substrate 141 b are etched in two steps. Namely,places shallowly etched in the metal substrate 141 b are used as thedriving electrodes 146 and detecting electrodes 147. Thereafter, otherplaces in the metal substrate 141 b are etched deeply, and places wherethe resin substrate 141 a is exposed will be the bottom face of therecess 145.

As stated above, the recess 145 may not be formed in the substrate body141 (for example, the height of the displacing portions 112 andconnecting portions 113 is set lower than the fixed portion 111). Inthat case, it is not necessary to perform the two-step etching forprocessing the metal substrate 141 b. The metal substrate 141 b may beused as a material for constituting the places corresponding to thebottom face of the frame portion 143, the driving electrodes 146 anddetecting electrodes 147.

As the reinforcing portion 142, a metal, for example, Fe—Ni type alloys,Fe—Ni—Co type alloys, more specifically stainless steel or Invar can beused.

For making the first substrate 140, a three-laminated (three-layered)material composed of the first metal substrate 142, the resin substrate141 a, and the second metal substrate 141 b can be used. Thethree-layered material can be formed, for example, by providing anadhesive layer between the resin substrate 141 a and the metal substrate141 b for laminating or adhering them together. Upon adhesion,optionally, pressurization using a press or heating may be employed.

In the case where the second metal substrate 141 b is etched in twosteps to form the driving electrodes 146 and detecting electrodes 147,the first metal substrate 142 will constitute the reinforcing portion142. As described above, when the recess 145 is not formed, the drivingelectrodes 146 and detecting electrodes 147 are formed by etching thesecond metal substrate (the places corresponding to the bottom face ofthe frame portion 143 are also made of the second metal substrate).

In place of the three-layered material, a two-layered material composedof the metal substrate 142 and resin substrate 141 may be also used. Insuch a case, the recess 145 will be formed by etching the resinsubstrate 141, followed by providing addition of the driving electrodes146 and detecting electrodes 147. Also, the metal substrate 142 willconstitute the reinforcing portion 142.

By using a layered material of the resin substrate 141 and metalsubstrate 142 as the first substrate 140, as compared to the case inwhich only a glass material is used for example, the height of thesubstrate 140 can be further reduced and thus a thinner type angularrate sensor 100 can be accomplished. Specifically, the height(thickness) of the substrate 140 can be set to approximately 60 to 90 μm(resinous material: 20 μm+metallic material: 40 to 70 μm), as comparedto 600 μm in the case of a substrate made of glass material. This isbecause the metallic materials have much better resistance againstbreakage than the glass materials.

The first substrate 140 and the first structure 110 can be connectedtogether using an adhesive or alloy.

For example, after providing a gold (Au) layer on the first structure110 while providing a tin (Sn) layer on the first substrate 140, the twocomponents are heated while being contacted with each other. As aresult, the gold and the tin will be changed into an alloy (gold-tineutectic alloy) to form an alloyed joined layer, thus the firstsubstrate 140 and the first structure 110 are joined together.

It is preferred that a barrier layer comprising Ni, Ti, Cr or the likeis further provided between the first structure 110 and the gold layer.Consequently, it can be prevented for the gold to diffuse into the firststructure 110 resulting in degradation of the properties of the angularrate sensor 100. The barrier layer may also serves as an adhesive foradhering the gold layer to the first structure 110 for forming the goldlayer on the first structure 110 (because of poor reactivity of gold,the bond strength of gold, for example, to silicon is quite low).

The second substrate 150 has an outer periphery of a substantiallyrectangular shape and includes a substrate body 151 and a reinforcingportion 152. The substrate body 151 has a frame portion 153 and a bottomplate portion 154. The substrate body 151 can be made by forming arecess 155 having a generally rectangular shape (for example, having awidth and height of 800 μm and a depth of 10 μm) in the substrate.

The frame portion 153 is formed of a substrate having outer and innerperipheries each having a generally square frame-like shape. The frameportion 153 has a shape corresponding to the shape of the pedestalportion 131, and is joined to the pedestal portion 131 by various means(for example, adhesives or alloys).

The bottom plate portion 154 is formed of a substrate having an outerperiphery with a generally square shape.

The aim of forming the recess 155 in the substrate 150 is to ensure toprovide a space required for the displacement of the weighting portions132. Alternatively, in place of forming the recess 155 in the secondsubstrate 150, or in addition to the recess 155, it is also possible tomake the pedestal portion 131 with a different height or thickness fromthat of the weighting portions 132. For example, making the thickness ofthe weighting portions 132 smaller than that of the pedestal portion 131can ensure to provide the space in which the weighting portions 132 canbe displaced.

The reinforcing portion 152 is formed of a substrate having an outerperiphery of a generally square shape, and is joined to the substratebody 151 by various means (for example, adhesives). The reinforcingportion 152 serves to enhance mechanical strength of the secondsubstrate 150 and reduce gas permeability of the second substrate 150.

For example, in the case where the main component of the substrate body151 is a resinous material (for example, a polyimide material), thethickness of the second substrate 150 must be increased to an extent soas to ensure to provide adequate strength of the substrate. In addition,permeation of an external gas through the second substrate 150 maydegrade the degree of vacuum in the interior of the angular rate sensor100.

To address such challenges, a material, for example, a metal having highstrength and non-gas-permeable properties can be used as the materialfor constituting the reinforcing portion 152 so as to ensure with easeto impart sufficient strength and non-gas-permeability to thereinforcing portion 152. As a result, it becomes easy to reduce thethickness of the second substrate 150 (i.e., miniaturize the angularrate sensor 100) as well as to decrease the gas permeability (i.e.,lengthen the life span of the angular rate sensor 100).

A driving electrode 156 is provided on the bottom plate portion 154 (onthe top face of the second substrate 150). A terminal 158 is connectedto the driving electrode 156. A through-hole is formed in the bottomplate portion 154 and reinforcing portion 152 for enabling electricconnection from the exterior of the angular rate sensor 100 to theterminal 158.

The driving electrode 156 is in a capacitive coupling relation to thedriving electrode 135, and the voltage to be applied during thecapacitive coupling will cause vibration of the displacing portions 112in the Z-axis direction. The details of this driving operation will bedescribed below. Since the second substrate 150 has a similar structureto the first substrate 140, the same material for constituting the firstsubstrate can also be used for the second substrate 150. Specifically, athree-laminated (three-layered) material composed of the first metalsubstrate 152, the resin substrate 151 a, and the second metal substrate151 b (or a two-layered material composed of the metal substrate 152 andresin substrate 151) can be used. In this respect, since the secondsubstrate 150 is not essentially different from the first substrate 140,the description of this matter is omitted here.

By using a layered material of the resinous material 151 and metallicmaterial 152 as the second substrate 150, as compared to the case inwhich only a glass material is used for example, the height of thesubstrate 150 can be further reduced and thus a thinner type angularrate sensor 100 can be accomplished. Specifically, the height(thickness) of the substrate 150 can be set to approximately 60 to 90 μm(resinous material: 20 μm+metallic material: 40 to 70 μm), as comparedto 600 μm in the case of glass materials. This is because the metallicmaterials have much better resistance against breakage than the glassmaterials.

As will be described below, when the produced angular rate sensor 100 istaken out from a semiconductor substrate by dicing, it is possible topress any suitable position of the bottom face of the substrate 150.This facilitates handling during production.

The first substrate 140 and the first structure 110 are connectedtogether using an adhesive or alloy.

In this respect, since the second substrate 150 is not essentiallydifferent from the first substrate 140, details of this matter isomitted here.

A sealed body 100A is constructed by the first substrate 140, fixedportion 111 of the first structure 110, pedestal portion 131 of thesecond structure 130, and second substrate 150, and as such thedisplacing portions 112 and weighting portion 132 can be moved in thesealed body 100 a.

(Operation of the Angular Rate Sensor 100)

The principle of detecting angular velocity using the angular ratesensor 100 is described. As described above, the mutually correspondingdriving electrodes 115, 146 and detecting electrodes 116, 147 arearranged between the first structure 110 and the first substrate 140.Also, the mutually corresponding driving electrodes 135, 156 areprovided between the second structure 130 and the second substrate 150.

(1) Vibration of the Displacing Portions 12

When a voltage is applied between the driving electrodes 115, 146, thesedriving electrodes 115, 146 are attracted to each other by the Coulombforce, and the displacing portions 112 (also the weighting portions 132)are displaced in the positive Z-axis direction. Also, when a voltage isapplied between the driving electrodes 135, 156, these electrodes 135,156 are attracted to each other by the Coulomb force, and the displacingportions 112 (also the weighting portions 132) are displaced in thenegative Z-axis direction. Namely, alternating application of thevoltage between the driving electrodes 115, 146 and between the drivingelectrodes 135, 156 causes the displacing portions 112 (also theweighting portions 132) to vibrate in both the Z-axis directions. Forthe application of voltage, a positive or negative direct-current waveform (a pulse wave form if including non-applied periods as well), ahalf-wave form or the like can be used.

The cycle of vibration of the displacing portions 112 depends on thecycle of switching the voltage. This switching cycle preferablyapproximates in some extent the natural frequency of the displacingportions 112. The natural frequency of the displacing portions 112depends on the elasticity of the connecting portions 113 and the mass ofthe weighting portions 132 and the like. If the cycle of vibrationapplied to the displacing portions 112 is not corresponding to thenatural frequency, the vibrational energy to be applied to thedisplacing portions 112 will diverge, thus lowering the energyefficiency.

(2) Generation of the Coriolis Force Due to Angular Velocity

When angular velocity ω is applied to the weighting portions 132(displacing portions 112) while the weighting portions 132 and thedisplacing portions 112 are moving at a velocity of vz in the Z-axisdirection, Coriolis force F works on these weighting portions 132.Specifically, corresponding to angular velocity ωx in the X-axisdirection and angular velocity ωy in the Y-axis direction, Coriolisforce Fy (=2×m×vz×ωx) in the Y-axis direction and Coriolis force Fx(=2×m×vz×ωy) in the X-axis direction will work on the weighting portions132, respectively (m is the mass of the weighting portions 132).

FIG. 10, correspondingly to FIG. 7, illustrates a cross sectionrepresenting a state of the angular rate sensor 100 when the Coriolisforce Fy (Fy=2×m×vz×ωx) due to angular velocity ωx in the X-axisdirection is applied to the sensor.

It is found that an inclination in the Y direction occurs of thedisplacing portions 112 by the effect of the Coriolis force Fy. In sucha manner, inclinations (displacements) in the X and Y directions of thedisplacing portions 112 will occur by the Coriolis force Fy, Fx due toangular velocities ωx, ωy.

(3) Detection of the Inclination of the Displacing Portions 112

The inclination of the displacing portions 112 can be detected by thedetecting electrodes 116, 147. When the Coriolis force Fy in thepositive Y-axis direction is applied to the displacing portions 112, thedistance between the detecting electrodes 116 c, 147 c will decrease,while the distance between the detecting electrodes 116 e and 147 e willincrease. As a result, the capacitance between the detecting electrodes116 c and 147 c becomes large, while the capacitance between thedetecting electrodes 116 e and 147 e becomes small. Namely, based on thedifference between the capacitance values obtained between therespective detecting electrodes 116 b to 116 e and 147 b to 147 e,changes in the inclinations of the displacing portions 112 in the X-axisand Y-axis directions are detected, and then obtained as detectedsignals.

As described above, the displacing portions 112 are vibrated in theZ-axis direction by means of the driving electrodes 115, 146 as well asthe driving electrodes 135, 156, and the inclinations of the displacingportions 112 in the X-axis and Y-axis directions are detected by meansof the detecting electrodes 116, 147 (the driving electrodes 115, 146 aswell as the driving electrodes 135, 156 serve as vibration impartingportions, while the detecting electrodes 116, 147 serve as displacementdetecting portions). As a result, it becomes possible to performmeasurement of the angular velocities ωy, ωx in the X-axis and Y-axis(two-axes) directions using the angular rate sensor 100.

(4) Removal of Bias Components From the Detected Signals

The signals outputted from the detecting electrodes 116, 147 includecomponents other than those resulting from the angular velocities ωy, ωxto be applied to the weighting portions 132. The signals also includecomponents resulting from accelerations αx, αy in the X-axis and Y-axisdirections to be applied to the weighting portions 132. The displacementof the displacing portions 112 is also generated due to the effect ofthese accelerations αx, αy.

To obtain the component of the angular velocity from the detected signalwhile removing the component of the acceleration, the difference ofcharacters of these components can be utilized. Namely, force Fω(=2×m×vz×ω) to be generated when angular velocity (ω) is applied to theweighting portions 132 (mass=m) depends on the velocity vz in the Z-axisdirection of the weighting portions 132. On the other hand, force Fα tobe generated when acceleration (α) is applied to the weighting portions132 (mass=m) does not depend on the vibration of the weighting portions132. That is, the component of the angular velocity in the detectedsignal is one type of amplitude components to be changed periodicallycorresponding to the vibration of the displacing portions 112, while thecomponent of the acceleration in the detected signal is one type of biascomponents which is not corresponding to the vibration of the displacingportions 112.

By removing the bias components from the detected signal, extraction ofthe angular velocity component from the detected signal, i.e.,measurement of the angular velocity can be performed. For example, bythe frequency analysis of the detected signal, a vibrational componentsimilar to the frequency of the displacing portions 112 can beextracted.

(Production of the Angular Rate Sensor 100)

The steps of producing the angular rate sensor 100 will be describedbelow.

FIG. 11 is a flow chart showing one example of a procedure for producingthe angular rate sensor 100. FIGS. 12 to 20, correspondingly to FIG. 7,illustrate cross sections each depicting a state of the angular ratesensor 100 in the production procedure of FIG. 11 (each corresponding toa cross section of the angular rate sensor 100 taken along line A1-A2 ofFIG. 1).

(1) Preparation of the Semiconductor Substrate W (Step S11, and FIGS. 12and 21)

As shown in FIG. 12, three layers, first, second, and third layers 11,12, 13 are laminated with one another to prepare a semiconductorsubstrate W.

FIG. 21 is a schematic diagram of the semiconductor wafer W. In thedrawing, the depiction of the first, second, and third layers 11, 12, 13is omitted. As shown in the drawing, the semiconductor substrate W isdivided into a plurality of regions A, each of which can produce theangular rate sensor 100. Namely, the angular rate sensors 100 areproduced collectively in large numbers (for example, several thousandsor several tens of thousands) on a sheet of semiconductor substrate W.

In FIG. 12, one of the regions A shown in FIG. 21 is depicted, and thisis also the case to the other FIGS. 13 to 20.

The first, second, and third layers 11, 12, 13 are employed forconstructing the first structure 100, joining portion 120, and secondstructure 130, consisting of silicon, silicon oxide, and silicon,respectively.

The semiconductor substrate W having such a three-laminated(three-layered) silicon/silicon oxide/silicon structure can be formed bylaminating a silicon oxide film and then a silicon film onto a siliconsubstrate (the so-called SOI substrate).

The purpose of forming the second layer 12 with a different materialfrom that of the first and third layers 11, 13 is to provide differentetching properties to the second layer 12 from those of the first andthird layers 11, 13, thereby to utilize the second layer 12 as anetching stopper layer. Namely, the second layer 12 serves as a stopperlayer in both etching processes wherein the first layer 11 is etchedfrom its top face and the third layer 13 is etched from its bottom face.

While in this example the first layer 11 and the third layer 13 areformed from the same material (silicon), all the first, second, andthird layers 11, 12, 13 may be formed from individually differentmaterials.

(2) Production of the First Structure 110 (Etching of the First Layer10, Step S12, and FIG. 13)

By etching the first layer 11, openings 114 are formed to construct thefirst structure 110. That is, using an etching process which is erosiveto the first layer 11 but not erosive to the second layer 12,predetermined regions (openings 114 a to 114 d) of the first layer 11are etched in the thickness direction until the top face of the secondlayer 12 is exposed.

In this case, a resist layer having a pattern corresponding to the firststructure 100 is formed on the top face of the first layer 11, followedby vertically downward erosion in the exposed regions uncoated with theresist layer. In this etching process, since the second layer 12 is noteroded, only the predetermined regions 114 (openings 114 a to 114 d) ofthe first layer 11 are removed.

FIG. 13 shows a state where the first structure 110 is formed byproviding the etching process as described above to the first layer 11.

(3) Production of the Second Structure 130 (Etching of the Third Layer13, Step S13, and FIG. 14)

By etching the third layer 13, openings 133 are formed to construct thesecond structure 130. That is, using an etching process which is erosiveto the third layer 13 but not erosive to the second layer 12,predetermined regions (openings 133) of the third layer 13 are etched inthe thickness direction until the bottom face of the second layer 12 isexposed.

In this case, a resist layer having a pattern corresponding to thesecond structure 130 is formed on the bottom face of the third layer 13,followed by vertically upward erosion in the exposed regions uncoatedwith the resist layer. In this etching process, since the second layer12 is not eroded, only the predetermined regions (openings 133) of thethird layer 13 are removed.

FIG. 14 shows a state where the second structure 130 is formed byproviding the etching process as described above to the third layer 13.

It is noted that the order of the etching process provided to the firstlayer 11 (Step S12) and the etching process provided to the third layer13 (Step S13) may be changed alternately. Otherwise, either of theetching processes may be performed first, or both of the processes maybe done simultaneously.

(4) Production of the Joining Portion 120 Between the First and SecondStructures 110, 130 (Etching of the Second Layer 12, Step S14, and FIG.15)

By etching the second layer 12, openings 120 a are formed to constructthe joining portion 120. That is, using an etching process which iserosive to the second layer 12 but not erosive to the first layer 11 andthe third layer 13, only the exposed portions of the second layer 12 areetched both in the thickness and layer directions.

In this etching process, there is no need to form a resist layer.Namely, the second structure 130, the remaining portion of the thirdlayer 13, serves as a resist layer for the second layer 12. This etchingprocess is applied to the exposed portions of the second layer 12, i.e.,the regions where the openings 133 are formed.

In the production procedure described above, the steps of forming thefirst structure 110 (Step S12) and the step of forming the secondstructure 130 (Step S13) should satisfy the following two conditions.

The first condition is to have directionality along the thicknessdirection of each layer. The second condition is ability to performetching that is erosive to the silicon layers but not erosive to thesilicon oxide layer. The first condition is necessary for formingopenings and grooves having predetermined sizes, while the secondcondition is necessary for utilizing the second layer 12 formed fromsilicon oxide as an etching stopper layer.

As the etching method satisfying the first condition, the InducedCoupling Plasma Etching Method (ICP) can be used. This etching method iseffective for forming deep grooves in the vertical direction, and is onetype of the etching methods commonly referred to as the Deep ReactiveIon Etching (DRIE).

In this method, an etching step for erosively digging a material layerin the thickness direction and a deposition step for forming a polymerwall over the side face of each of the so formed holes are repeatedalternately. In such a way, since the side face of each of the holes isprovided with and protected by such a polymer wall successively, erosiononly in the thickness direction can be progressed.

In order to perform the etching satisfying the second condition, anetching material having the etching selectivity between the siliconoxide and silicon can be used. For example, a mixed gas of the SF gasand O₂ gas in this etching step, while the C₄ F₈ gas may be used in thedeposition step.

In the etching step applied to the second layer 12 (Step 14), theetching method should meet the following two conditions. The firstcondition is to have directionalities both in the thickness directionand the layer direction. The second condition is ability to performetching that is erosive to the silicon oxide layer but not erosive tothe silicon layers.

The first condition is necessary for preventing from the degree offreedom in the displacement of the weighting portions 132 to berestricted by the silicon oxide layer remaining at unnecessary regions.The second condition is necessary for preventing the erosive effect towork on the first structure 110 and the second structure 130 formed fromsilicon, because the predetermined shapes in these structures 110, 130have been already completed.

As the etching method satisfying both the first and second conditions, awet etching method utilizing a buffered hydrofluoric acid (a mixedsolution of HF:NH₄F=1:10) as an etching solution can be used. Also, adry etching method according to the RIE method utilizing a mixed gas ofCF₄ gas and O₂ gas is applicable.

(5) Formation of the Electrodes (Step S16, and FIG. 16)

The driving electrodes 115 and the detecting electrodes 116 are formedon the displacing portions 112, and the driving electrode 135 is formedon the rear face of the weighting portion 132 a. The formation can beachieved by film-forming of an electrode material (e.g., copper) andpatterning (an etching process using a mask).

(6) Joining of Layered Products C1, C2 in Which the First and SecondSubstrates 140, 150 are Formed (Step S17, and FIG. 17)

1) Forming of the First and Second Substrates 140, 150 in LayeredProducts C1, C2

As layered products C1, C2, three-layered materials composedrespectively of the first metal substrates 142, 152, resin substrates141 a, 151 a, and second metal substrates 141 b, 151 b can be used.

The first substrate 140 can be formed by two-step etching of the secondmetal substrate 141 b of the three-layered material to form the recess145, driving electrodes 146 and detecting electrodes 147. The secondsubstrate 150 can be formed by two-step etching of the second metalsubstrate 151 b of the three layered material to form the recess 155 anddriving electrode 156.

As mentioned above, the driving electrodes 146 and detecting electrodes147 may be formed by etching the second metal substrate 141 b withoutforming the recess 145.

Also in the layered products C1, C2 are formed through-holes throughwhich electrical connections from the outside can be provided to theterminals 148, 149, 158 of the electrodes 146, 147, 156.

In this stage (before a dicing process described below), the first andsecond substrates 140, 150 are formed on the layered products C1, C2,respectively, in large numbers, and not yet separated into individualsubstrates 140, 150.

2) Joining the First Substrate 140 to the First Structure 110, and theSecond Substrate 150 to the Second Structure 130

The first structure 110 and the first substrate 140, and the secondstructure 130 and the second substrate 150 are joined together,respectively.

In this case, an adhesive or alloy can be utilized. For example, joiningby using an alloy is carried out as follows. While the joining of thefirst substrate 140 to the first structure 110, and the second substrate150 to the second structure 130 are commonly carried out successively,the two joining operations are described together because thesesubstrates and structures can be joined in the same manner,respectively.

Formation of Metal Films on the Bottom Face of the Substrate 140 and onthe Top Face of the Substrate 150

Films of a first metal (for example, tin) are formed on the bottom faceof the substrate 140 and on the top face of the substrate 150.

Formation of Metal Firms on the Top Face of the First Structure 110 andon the Bottom Face of the Second Structure 130 (Metallization)

Films of a second metal (for example, gold) are formed on the top faceof the first structure 110 and on the bottom face of the secondstructure 130, the second metal being capable of creating an alloy withthe first metal. In this case, prior to forming a gold film on the topface of the first structure 110 and on the bottom face of the secondstructure 130, a film of, for example, Ni, Ti or Cr is formed as abarrier layer.

Joining of the First Substrate 140 to the First Structure 110 and theSecond Substrate 150 to the Second Structure 130

Contacting the tin layer on the bottom face of first substrate 140 tothe gold layer on the top face of first structure 110 while contactingthe tin layer on the top face of second substrate 150 to the gold layeron the bottom face of second structure 130, respectively, thesecontacted materials are heated at 200 to 250° C. As a result, alloyingof the gold and tin layers occurs to form a gold-tin alloyed layer, thusjoining the first substrate 140 to the first structure 110 and thesecond substrate 150 to the second structure 130.

(7) Dicing of the Semiconductor Substrate W (Step S17, and FIGS. 18 to20, and 22)

1) Connection to a Dicing Pad 21

A dicing pad is connected to the bottom face of the layered product C2.The dicing pad 21 is an adhesive film adapted to fix the angular ratesensors 100 when the sensors 100 are cut by dicing from thesemiconductor substrate W and layered products C1, C2. On a surface ofthe dicing pad 21, an adhesive material is coated, the adhesionproperties of which material will be lowered by irradiation ofultraviolet rays.

FIG. 22 is a schematic diagram showing a state where the dicing pad 21is connected to the semiconductor substrate W and layered products C1,C2, in which the angular rate sensors 100 are formed in large numbers.

2) Formations of Notches

Notches are formed by cutting the semiconductor substrate W and layeredproducts C1, C2 using a dicing saw or the like. In this case, a coolantis used for reducing the heating of the cut positions (FIG. 18).

3) Removal of the Angular Rate Sensors 100

With the bottom face of the second substrate 150 being pushed byprojecting pins 22 and each angular rate sensor 100 being lifted fromthe substrate W, the angular rate sensor 100 is sucked by a suckingmouth 24 of a vacuum chuck 23 (FIG. 19, 20). At that time, byirradiation of ultraviolet (UV) rays to the adhesive material of thedicing pad 21, the adhesion properties is lowered, thereby providingeasy separation of the angular rate sensor 100 from the dicing pad 21.

The projecting pins 22 can push any positions of the bottom face (thewidth D in FIG. 19) of the substrate 150. The second substrate 150 isformed of a layered product composed of a resin and a metal and thus hasa sufficient strength. Accordingly, the angular rate sensor 100 is notbroken by the pushing force due to the projecting pins 22.

If the angular rate sensor 100 were removed in a state where the secondsubstrate 150 is not connected thereto, the area that the projectingpins 22 could push is limited to the area of the pedestal portion 131(the width DO in FIG. 19), thus requiring quite minute control of theprojecting pins 22. Namely, should the projecting pins 22 push directlythe weighting portions 132, the connecting portions 113 would be broken.

In addition, should the substrates 140, 150 be formed from a glassmaterial, it would be difficult to make the substrates 140, 150relatively thin, and therefore production of a thinner angular ratesensor 100 would be quite difficult.

According to the present invention, by using layered materials composedof a resin and a material for forming the first and second substrates140, 150, the reliability of sealing the angular rate sensor 100 can beassured, and production of a significantly thinner angular rate sensor100 and enhancement of its productivity can be accomplished.

OTHER EMBODIMENTS

The embodiments of the present invention are not limited to thosedescribed above, and further extensions and modifications can be made.It should be construed that such extended and modified embodiments fallin the technical scope of the present invention.

1. An angular rate sensor comprising: a first structure which includes afixed portion having an opening, a displacing portion placed in theopening and configured to be displaced relative to the fixed portion,and a connecting portion adapted to connect the fixed portion and thedisplacing portion, and is formed of a substrate composed of a firstsemiconductor material; a second structure which includes a weightingportion respectively joined to the displacing portion, and a pedestalportion arranged to surround the weighting portion and joined to thefixed portion, and is laminated in place on the first structure andcomposed of a second semiconductor material; a first substrate laminatedon the first structure; a second substrate laminated on the secondstructure; a vibration imparting portion adapted to impart vibration tothe displacing portion of the first structure; and a displacementdetecting portion adapted to detect displacement of the displacingportion; wherein: the first substrate, the fixed portion, the pedestalportion, and the second substrate form a sealed body together such thatthe displacing portion and the weighting portion can be moved in thesealed body; the first substrate includes a first metal layer and afirst insulating layer laminated on the first metal layer, the firstinsulating layer including a first recess, and being connected to thefixed portion; and the second substrate includes a second metal layerand a second insulating layer laminated on the second metal layer, thesecond insulating layer including a second recess, and being connectedto the pedestal portion.
 2. The angular rate sensor according to claim1, wherein each of the first insulating layer of the first substrate andthe second insulating layer of the second substrate is composed of amaterial capable of being etched.
 3. The angular rate sensor accordingto claim 1, wherein either of the first insulating layer of the firstsubstrate or the second insulating layer of the second substrate has athird metal layer formed thereon.
 4. The angular rate sensor accordingto claim 3, wherein the vibration imparting portion is formed of thethird metal layer.
 5. The angular rate sensor according to claim 3,wherein the displacement detecting portion is formed of the third metallayer.
 6. The angular rate sensor according to claim 1, wherein each ofthe first semiconductor material of the first structure and the secondsemiconductor material of the second structure is formed from silicon.7. The angular rate sensor according to claim 1, wherein a joiningportion is provided between the first structure and the secondstructure.
 8. The angular rate sensor according to claim 7, wherein eachof the first semiconductor material of the first structure and thesecond semiconductor material of the second structure is formed fromsilicon while the joining portion is formed from silicon oxide.